Evaluation of a rapid antigen test using a point of care real-time RT-PCR as a comparator for the detection of SARS-CoV-2

A rapid antigen test (RAT) was compared with a point-of-care real-time RT-PCR for the diagnosis of COVID-19 using “50 nasopharyngeal swabs (25 positive and 25 negative by POC-rtRT-PCR)”. The samples were collected from symptomatic patients at the Teaching Hospital, Peradeniya (March–August 2021) and tested using the STANDARD™ Q COVID-19 Ag RAT. The diagnostic performance of the RAT was assessed by calculating sensitivity, specificity, positive predictive value (PPV), and negative predictive value (NPV) using Microsoft Excel 2010 and MedCalc software. The RAT showed 100% sensitivity for high viral loads (Ct ≤ 20.3) with 96% specificity. Sensitivity dropped to 48% for samples with low viral loads (Ct = 20.9–33.0). The RAT was highly reliable at detecting high viral loads but showed reduced sensitivity at lower viral loads, making it most suitable for detecting highly infectious COVID-19 cases.